For over 25 years, common belief has been widely viewed as necessary for joint behavior. But this is not quite correct. We show by example that what can naturally be thought of as joint behavior can occur without common belief. We then present two variants of common belief that can lead to joint behavior, even without standard common belief ever being achieved, and show that one of them, action-stamped common belief, is in a sense necessary and sufficient for joint behavior. These observations are significant because, as is well known, common belief is quite difficult to achieve in practice, whereas these variants are more easily achievable.

翻译：25年多来，共同信念一直被视为联合行为的必要条件，但这一观点并不完全正确。我们通过实例证明，在没有共同信念的情况下，自然可被视作联合行为的现象仍可能发生。接着，我们提出两种无需达到标准共同信念即可促成联合行为的共同信念变体，并证明其中一种——行动标记共同信念——在某种意义上对联合行为既必要又充分。这些观察具有重要意义，因为众所周知，共同信念在实践中极难实现，而本文提出的变体则更易达成。